International expert warns Central Otago gold mine design is ‘riskiest’ option
Wednesday, 17 June 2026
Storing 22 million tonnes of toxic mining waste in a dam has been described as “a very risky option” by an international expert.
On Tuesday, Aachen University professor Bernd Lottermoser told a Fast-track panel considering Santana Minerals’ proposal to build a large gold mine near Cromwell there were other options for storing waste from the mine.
These included putting it back in the pits dug to extract gold, mixing it with concrete and pumping it into the mine’s underground tunnels, and extracting water from it and disposing of it elsewhere.
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Santana has described its Bendigo-Ophir Gold Project near Cromwell as New Zealand’s most significant gold find in 40 years. Over the mine’s suggested 14 years of operation, waste from processing the ore needs to be disposed of.
The Australian company plans to build a 2km-long storage dam in a stream bed, where the wet tailings slurry would be stored forever.
The mine proposal has become extremely controversial, and is being considered under the Fast-track process by a seven-member panel, which is in its second week of hearings in Wellington, with experts giving evidence about contentious issues.
Lottermoser said Santana’s “wet tailings” plan for disposing of mining waste was the “riskiest option” available, and he questioned why it wasn’t adopting other emerging international technologies, including those promoted by some of the world’s largest mining companies.
“I don’t see the data, I don’t see the evidence, I don’t see the knowledge that you can claim that this is the best option,” Lottermoser told the panel.
But Santana’s expert, Trevor Matuschka, said what the company was proposing was the most common form of tailings disposal, and posed an extremely low risk to the environment.
While other more expensive techniques may have lower risk, Matuschka said the risks in Santana’s plan were acceptable.
As well as the dam walls containing the tailings, rock dug from the mining pits would be used to provide extensive buttressing, further reducing the possibility of the dam failing and releasing toxic waste.
Any contaminated water seeping from the dam would be captured by drains as it moved down the valley.
Matuschka said the the dam’s design would have to meet building codes, would be peer reviewed, and was designed to withstand a 1:10,000 year earthquake, and cope with more than a year’s rainfall over three days.
Tailings storage expert Steve Emerman, an American professor appearing for Sustainable Tarras, which is opposing the mine, pointed to the large amounts of rock Santana will dig up in order to extract gold.
“And that left me asking, why are we doing this? Why are we doing open pit mining here instead of underground mining or some other mining method?
“Where’s the study that explains why underground mining is not feasible?” Emerman asked.
Santana will dig four open pits, and commence some underground mining after seven years.
Other experts also raised the issue of gaps in evidence, saying Santana hadn’t provided information about its consideration of alternative mining or tailings storage options.
Another Sustainable Tarras expert, geologist Alex McAlpine, said he would have expected expert discussion about open pit mining versus underground mining to have occurred much earlier.
“It seems as though we’re making a decision on a mine that has had essentially one concept of design.”
He understood this might be for economic reasons, as under the current plan, Santana would be able to extract gold almost as soon as it began digging, whereas underground mining would mean a slower return on investment.
The Fast-track panel will hear from economic experts on Wednesday about the proposal’s suggested benefits for the region and country.
It is due to make a final decision on whether the mine is given the green light or not, by October 29.